1. Field of Invention
The present invention relates to a technique for real time air measurement in wet concrete; more particularly related to a technique for real time air measurement in wet concrete in order to control the amount of air in a mixture of concrete.
2. Description of Related Art
In the prior art, the use of a method for the determination of the flow rate of the medium through a measurement of the velocity of convecting vortical pressure instabilities, and the composition of a two-phase flow through the determination of the speed of sound of the medium, are known. As the composition of the flow varies between the two extremes of 100% of one fluid to 100% of the other, the speed of sound varies in a deterministic way between the values of sound speed in the two respective materials. In the known techniques, the determination of the speed of sound was made using ‘passive’ listening of the sound propagating in the flow stream.
In the prior art, a number of techniques have been developed that rely on measuring the speed of sound through a material flowing through a pipe. These techniques include using a known SONAR-based GVF meter, density meter and potential mass fraction meter. In these techniques, a passive array-based sensor system is used to detect the presence and speed of acoustics traveling through the materials contained within a pipe. These materials can range from single phase homogeneous fluids to two or three phase mixtures of gases, liquids and solids. Since the measurements system is passive it relies on acoustics produced externally for the measurement. These acoustics can often times come from other equipment in or attached to the pipe such as pumps or valves.
Moreover, in these known techniques many times chemical additives may be added, including to a known flotation process in mineral processing to aid in the separation of the ore. The chemicals, known as frothers, control the efficiency of the flotation process by enhancing the properties of the air bubbles. An important parameter in flotation optimization is the gas volume fraction within a flotation cell. U.S. Pat. No. 7,426,852 B1, which is hereby incorporated by reference in its entirety, discloses approaches to make this measurement, and discloses a technique whereby the speed of sound in the aerated fluid is locally measured using a waveguide (pipe) in conjunction with a SONAR-based array. From the speed of sound measurement, the gas volume fraction can be calculated.
By way of example, see other techniques related to the use of such SONAR-based technology disclosed, e.g., in whole or in part in U.S. Pat. Nos. 7,165,464; 7,134,320; 7,363,800; 7,367,240; and 7,343,820, all of which are incorporated by reference in their entirety.
Moreover, air is a very important component of many materials, such as viscous liquids, slurries or solids, and mixtures of concrete. In particular, air is a critical ingredient when making concrete because it greatly improves the cured product damage resistance to freeze/thaw cycles. Chemical admixtures are typically added during mixing to create, entrain and stabilize billions of small air bubbles within the concrete. However, the entrained air in concrete has the disadvantage of reducing strength so there is always a trade-off to determine the right amount of air for a particular application. In order to optimize certain properties of concrete, it is important to control the entrained air present in the wet (pre-cured) concrete. Current methods for measuring the entrained air can sometimes be slow and cumbersome and additionally can be prone to errors. Moreover, the durability of concrete may be enhanced by entraining air in the fresh mix. This is typically accomplished through the addition of chemical admixes. The amount of admix is usually determined through empirical data by which a “recipe” is determined. Too little entrained air reduces the durability of the concrete and too much entrained air decreases the strength. Typically the nominal range of entrained air is about 5-8% by volume, and can be between 4% and 6% entrained air by volume in many applications. After being mixed in the mixer box, the concrete is then released to the truck. The level of entrained air is then measured upon delivery of the mix to the site. The draw back of the current method is that the mix is committed to the truck without verification of that the air level in the mix is within specification.
The aforementioned U.S. patent application Ser. No. 13/583,062 (WFVA/CiDRA file nos. 712-2.338-1/CCS-0033, 35,40, and 45-49) discloses techniques for real time air measurement in wet concrete in concrete a rotary drum mixer, including implementing sensing technology in a hatch cover, as well as a stationary concrete mixer using an integrated sound source and two receivers, using SONAR-based technology developed and patented by the assignee of the instant patent application as well as that application.